Organization and Summary of Significant Accounting Policies - Basis of Presentation (Details)	12 Months Ended
Dec. 31, 2020 location
First Hawaiian, Inc. (FHI)
Capitalization
Outstanding common stock owned (as a percent)	100.00%
First Hawaiian Bank (FHB)
Capitalization
Number of Branches	54

Represents the number of branches that offers a comprehensive suite of banking services to consumer and commercial customers including loans, deposit products, wealth management, insurance, trust, retirement planning, credit card and merchant processing services.

No definition available.

Name:	fhb_NumberOfBranches
Namespace Prefix:	fhb_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration